G-force refers to either the force of gravity on a particular celestial body or the force of acceleration anywhere. It is measured in g's, where 1 g equals the force of gravity at the Earth's surface (9.8 meters per second per second). As Einstein realized, the force of gravity and the forces of acceleration are mutually indistinguishable on the subject; a person in an opaque box experiencing a g-force would be unable to tell whether its origin lies in acceleration through space or a gravitational field, unless he had some way of seeing outside the box. The analysis of this force is important in a variety of scientific and engineering fields, especially planetary science, astrophysics, rocket science, and the engineering of various machines such as fighter jets, race cars, and large engines.

Humans can tolerate localized g-forces in the 100s of g's for a split second, such as a slap to the face. Sustained forces above about 10 g can be deadly or lead to permanent injury, however, although there is considerable variation among individuals when it comes to their tolerance. Race car drivers have survived instantaneous accelerations of up to 214 g during accidents. In rocket sled experiments designed to test the effects of high acceleration on the human body, Colonel John Stapp in 1954 experienced 46.2 g for several seconds. Usually, accelerations beyond 100 g, even if momentary, are fatal.

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In everyday life, humans experience g-forces stronger than 1 g. A typical cough produces a momentary force of 3.5 g, while a sneeze results in about 3 g of acceleration. Roller coasters are usually designed not to exceed 3 g, although a few notable exceptions produce as much as 6.7 g. Slight increases are experienced in any moving machinery, such as cars, trains, planes, and elevators. Astronauts in orbit experience 0 g, called weightlessness.

G-force varies on different planets or celestial bodies. When an object has a greater mass, it produces a higher gravitational field, resulting in higher g-forces. On the Moon, it's about 1/6 g, and on Mars, about 1/3 g. On the Martian satellite Deimos, only 8 miles (13 km) in diameter, the gravity is about 4/10,000ths of a g. In contrast, the surface of Jupiter experiences about 2.5 g. This is smaller than it seems it should be because Jupiter's low density causes its surface to be very far from its primary concentration of mass at the core. On the surface of a neutron star, a degenerate star with a density similar to the atomic nucleus, the surface gravity is between 2×1011 and 3×1012 g's.

Discuss this Article

@anon302147: The object would move off at a tangent (straight line) to the circle it is moving in. However it would curve down towards the ground.

The acceleration can be dynamically resolved into two directions, horizontally (X) and vertically (Y).

Horizontal velocity would fall due to air resistance, but if it was in a vacuum it would continue to move with a constant velocity in the X direction.

Vertical velocity & acceleration would be caused by gravity, acceleration of its mass times acceleration due to gravity (m x 9.81m/s) minus the air resistance would give the force, then convert that back to velocity using newtons laws.

anon302147Post 16

If you were to drop an item in a centrifuge producing 9 gs what would happen to the item? Would it just fall like normal?

anon284810Post 14

Quick question: What is the G of an object that just passed through a tunnel through the center of the Earth? If falling at 1 G, when getting the the surface at the other side, is it 1, 2 or zero G?

anon260406Post 13

Does 'G' vary with the height or does it remain the same at all altitudes?

anon164232Post 11

If an astronaut in a space vehicle is in space outside of the gravitational field of any space mass, is it possible for the astronaut to "accelerate" with suffering a "g force"?

anon112652Post 10

Can anyone guide me how to get a display g- force of a revolving object at a speed of approx. 150 Rpm

anon108539Post 9

What is the maximum g force on an object dropped from zero height? The object's total weight is suspended at no height and dropped/ I have been told the answer is two Gs.

anon59105Post 7

i think it's a very good article, you know.

anon58448Post 6

g force, i would suppose, has to do with inertia exerted by gravity. As gravity pulls and/or pushes an object the inertia is sometimes so intense that blood flow from the body cannot overcome its ability to push blood to the brain and other organs. it taxes the heart to over come the initial pulling of sudden g forces multiplied by speed of force.

anon47774Post 4

I think I need more specific details about the g-force.

anon34632Post 3

@nicktals4: It is simply 1. It is accelerating from gravity itself.

nicktals4Post 2

I would like to know how to calculate the G force of a box weighing 18 lbs when it fall from 3 feet.

In Gs.

anon12715Post 1

Hello i would like to convert g-force to lbs of impact force and mph, is this possible? would be great to find news about g-force in relation to cornering forces and collision analysis! for example how dangerous and hard is a strike/hits of 40 g?

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